Database Product Description
- Host Organism
- Zea mays (Maize)
- Glufosinate ammonium herbicide tolerance and fertility restored.
- Trait Introduction
- Microparticle bombardment of plant cells or tissue
- Proposed Use
Production for human consumption and livestock feed.
- Product Developer
- Pioneer Hi-Bred International Inc.
Summary of Regulatory Approvals
Summary of Introduced Genetic Elements Expand
Characteristics of Zea mays (Maize) Expand
Donor Organism Characteristics Expand
Modification Method Expand
Characteristics of the Modification Expand
Environmental Safety Considerations Expand
Food and/or Feed Safety Considerations Expand
Maize (Zea mays L.), or corn, is is grown primarily for its kernel, which is largely refined into products used in a wide range of food, medical, and industrial goods.
Only a small amount of whole maize kernel is consumed by humans. Maize oil is extracted from the germ of the maize kernel and maize is also a raw material in the manufacture of starch. A complex refining process converts the majority of this starch into sweeteners, syrups and fermentation products, including ethanol. Refined maize products, sweeteners, starch, and oil are abundant in processed foods such as breakfast cereals, dairy goods, and chewing gum.
In the United States and Canada maize is typically used as animal feed, with roughly 70% of the crop fed to livestock although an increasing amount is being used for the production ot ethanol. The entire maize plant, the kernels, and several refined products such as glutens and steep liquor, are used in animal feeds. Silage made from the whole maize plant makes up 10-12% of the annual corn acreage, and is a major ruminant feedstuff. Livestock that feed on maize include cattle, pigs, poultry, sheep, goats, fish and companion animals.
Industrial uses for maize products include recycled paper, paints, cosmetics, pharmaceuticals and car parts.
The maize lines 676, 678, and 680 were genetically engineered to express male sterility and tolerance to glufosinate ammonium, the active ingredient in phosphinothricin herbicides (Basta®, Rely®, Finale®, and Liberty®). Glufosinate chemically resembles the amino acid glutamate and acts to inhibit an enzyme, called glutamine synthetase, which is involved in the synthesis of glutamine. Essentially, glufosinate acts enough like glutamate, the molecule used by glutamine synthetase to make glutamine, that it blocks the enzyme's usual activity. Glutamine synthetase is also involved in ammonia detoxification. The action of glufosinate results in reduced glutamine levels and a corresponding increase in concentrations of ammonia in plant tissues, leading to cell membrane disruption and cessation of photosynthesis resulting in plant withering and death.
Glufosinate tolerance in these maize lines is the result of introducing a gene encoding the enzyme phosphinothricin-N-acetyltransferase (PAT) isolated from the common aerobic soil actinomycete, Streptomyces viridochromogenes, the same organism from which glufosinate was originally isolated. The PAT enzyme catalyzes the acetylation of phosphinothricin, detoxifying it into an inactive compound. The PAT enzyme is not known to have any toxic properties.
The male-sterile trait was introduced by inserting a bacterial gene encoding the enzyme DNA adenine methylase (DAM). Expression of the Escherichia coli dam gene in specific plant tissues results in the inability of the transformed plants to produce anthers or pollen, resulting in a male-sterile plant. The PAT enzyme was used as a selectable marker enabling identification of transformed plants during tissue culture regeneration, and as a field selection method to identify the male-sterile lines prior to flowering. Under field conditions, plants that were not male-sterile could be eliminated by application of the herbicide glufosinate ammonium. The novel hybrid system provided an efficient and effective way to identify male-sterile plants for use in hybrid seed production.
The maize lines 676, 678, and 680 have been field tested in the major maize growing regions of the United States since 1995. Field data regarding seed germination rates, yield characteristics, disease and pest susceptibilities, compositional analyses, and numerous other reports supported the conclusion that maize lines 676, 678, and 680 were as safe to grow as any other male sterile maize and would not present a plant pest risk. It was demonstrated that the transformed maize lines did not exhibit weedy characteristics, or negatively affect beneficial or non-target organisms. Maize lines 676, 678, and 680 were not expected to impact on threatened or endangered species.
Maize does not have any closely related species growing in the wild in the continental United States and Canada. Cultivated maize can naturally cross with annual teosinte (Zea mays ssp. mexicana) when grown in close proximity, however, these wild maize relatives are native to Central America and are not naturalized in North America. Additionally, multiple barriers, including sterility of the maize lines 676, 678, and 680, ensured that gene flow from these transformed lines into wild or cultivated sexually-compatible plants was extremely unlikely. Gene exchange between maize lines 676, 678, and 680 and maize relatives was determined to be negligible in managed ecosystems, with no potential for transfer to wild species in Canada and the United States.
In an assessment of food and livestock feed safety, forage and grain from these male-sterile lines were analyzed for nutritional composition and compared to the nutritional composition of non-transgenic inbred parental lines. Proximate, fatty acid, and amino acid analyses were performed and in each case there were no significant differences noted between the transgenic and non-transgenic control lines. The use of maize products derived from lines 676, 678, and 680 was not anticipated to have any significant impact on the nutritional quality of the food supply.
Previous studies have demonstrated that the PAT protein has a very low potential to be toxic or allergenic. The enzyme possesses none of the physiochemical characteristics commonly associated with known toxins or allergens, such as resistance to thermal or proteolytic degradation, and its amino acid sequence does not show homology with the sequences of known protein toxins and allergens.
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This record was last modified on Wednesday, February 25, 2015